1. Field of the Invention
The present invention relates generally to a method and an apparatus for discharging air from and supplying brake liquid to a brake system, and more particularly, to a brake system with an anti-lock brake device.
2. Description of Prior Art
Preventing the presence of air in a vehicle brake liquid passage in a vehicle brake system is important in order to improve brake performance. One practical way of eliminating air from such a system is to discharge air from the brake liquid passage by a vacuum pump before supplying or charging brake liquid to the system, as shown in Japanese Utility Model Laid-Open Application No. 60-35099.
Another practical way is to adopt a pumping operation which repeats depressing and releasing of a brake pedal so that brake liquid is filled up into the brake system without being compressed. Air mixed and compressed in the brake liquid can be removed from an inside wall of a wheel cylinder by expansion of the wheel cylinder, as shown in the Japanese Patent Laid-Open Application No. 62-16393.
An anti-lock brake device which prevents a vehicle from skidding or slipping by precisely controlling brake application to the wheels of the vehicle so that they do not lock has recently been introduced. This anti-lock brake device has complicated brake piping which consists, of main brake piping connecting a master cylinder and a wheel cylinder, and sub-brake piping interposed in the main brake piping and controlling the liquid pressure of the main brake piping. In this anti-lock brake device, air in the main brake piping cannot be removed as expected, even if above-mentioned methods are used, because of complicated piping. This can cause serious braking problems.